2004 Official factory service manual for Yamaha YFZ450S ATV Quad., Page 326Get this manual
STARTER MOTOR
5Measure: brush length Out of specification Replace the brushes as setBrush length wear limit 3.5 mm (0.14 in) 6Measure: brush spring force Out of specification Replace the brush springs as setBrush spring force 7.169.52 (730971 gf, 25.7734.27 oz) 7Check: gear teeth Damagewear Replace the gear8Check: bushing bearing oil seal Damagewear Replace the defective part(s)